In computer systems having interconnected processors and peripheral devices it is important to assure that system time is accurately and synchronously tracked. In systems wherein each processor is provided with associated time keeping hardware, it is desirable to change the time setting in a synchronized manner across all processors in the system. Otherwise it may be that a program or process has differing time values returned to it as it runs on various processors in the system. There may be many reasons for such discrepancies. Most often some change has occurred in the time adjustment of one processor that has not been propagated to the other(s).
In such systems, it is common to use control hardware to inhibit updating the time keeping hardware for a given processor while software makes an adjustment. The process is repeated for each processor in the system at its next control interval. Every processor, having applied the same adjustment to its time keeping hardware (or clock), should have the same clock time value. However, a discrepancy may still arise since a program or process is likely to have interrogated a clock before all processor clocks have been adjusted.
Further difficulty arises from such stop-start operation of clock hardware since processor clocks are not stopped and started evenly, with small variations in elapsed time during adjusting occurring. Therefore, over time and many stop-starts, variances become cumulative.
It is therefore desirable to assure that system time may be kept accurately and synchronously across a plurality of interconnected processors without the shortcomings noted above.